Seismic streamers are towed by a vessel in a marine environment such as an ocean. Each seismic streamer (cable) includes a series of the geophones or hydrophones (receivers) that receive seismic signals and convert them into electrical or other signals. The receivers arranged along the seismic streamers record seismic signals resulting from a reflection of a seismic source signal transmitted into the underwater environment below the seismic streamers. The seismic source signal may originate from the vessel, for example (e.g., based on gun array). The seismic streamers extend behind the vessel and can be several to tens of kilometers in length. Thus, the seismic streamers are unlikely to be linear but, instead, have shapes affected by factors like wind speed, direction, and marine current, for example. The seismic streamers are typically fashioned with the receivers arranged at regular intervals along each seismic streamer.
Seismic streamers also have acoustic pods that both send and receive coded pulses through the water. These coded pulses allow determination of the travel time between different acoustic pods and form a network of ranges. By using the acoustic pods with global positioning system (GPS) receivers on the front and tail end of the streamers and the gun array, the network of ranges from the acoustic pods can be solved to determine the location of the streamers under the water.
In addition to the receivers and the acoustic pods, each seismic streamer also includes one or more magnetic compasses arranged along its length. Each magnetic compass measures the direction of the earth's magnetic field at specified time intervals. This information, along with the knowledge of the location of each magnetic compass along the respective seismic streamer and information from the receivers, facilitates estimation of the graphic shape of each streamer over time. This graphic shape in turn can be used to determine the location of each receiver relative to the vessel as a check of the acoustic ranges or as a replacement for acoustic ranges depending on the level of confidence for the different information provided.